What Is Colour?




I used to tell my students, "Colour has only two attributes or properties, physical and psychological.  We can re-name them, measure and pleasure."

Our sensitivity to color derives from the sensitivity of the rods and cones on the surface of the retina in the eye to energies of wavelength 400nm (blue) to 700nm (red).  So when we measure color we record the way in which the particles in the object have interacted with the energy.  If all of the energy is absorbed, the object appears black.   If all of the energy is reflected, the object appears white.   If some of the energy is absorbed, the object appears coloured.

So when you “see” an object, your eyes are stimulated by the waves of energy coming from the object.  The wavelength and frequency of theses waves determines the “color” that you “see”.


colour light waves


We cannot synthesize color easily.  In print or on the screen, we rely on the model of the physicist James Clerk Maxwell, who suggested that we could synthesize from the addition of varying amounts of Red, Green and Blue light.

There have been many ways in which people have suggested that color can be made from RED GREEN and BLUE. The next image from http://www.codeproject.com is one such method devised by Albert Munsell, called the Munsell Colour Wheel.

Using 3D co-ordinates a color can be defined.  The definition is made in terms of hue (color), chroma (saturation), and value (amount of black and white added). This is a measure of “pleasure of color”.

The Munsell system defines color along these three measurement axes.

Black and white and grey are not colors.  They are brightness values or modifiers.  They are modifiers for the colors into which they are mixed, or onto which they have been layered.


colour munsell


However the color you get in your camera sensor; your RAW file; your post-processing software; your monitor; your print, are all different because of the way in which the color is synthesized and defined by the software.  This is “color space” or gamut.

Gamut is based on the ICI System of colour definition ( ICI - an organization who defined color in this way.  I assume chemical company for dyes.).  This is defined in terms of the dominant wavelength, excitation purity and luminous intensity.  This is a measure of “measure of colour”.

Gamut - is this representation of these definitions in a 2D or 3D space, mathematically speaking.  No two Gamuts are the same.  The gamut for a monitor is a smaller space than PANTONE inks so you get a wider range of color in your printed images using PANTONE inks that you can see on your monitor.


colour gamut


color In Your Software


Color is a property of all objects, and it is one of the properties that designers and advertisers use to draw your eye to the object.


colour colured image


In Paint Shop Pro or your photo processing software, call up a new page on which to paint, select a brush with which to paint and open the color dialogue box.

Manually, type in the values of Red (255), Green (0), and Blue (0).  Now adjust the values to Red (255), Green (255) and Blue (0).  When you change the values the foreground color changes.

The color changes from red to yellow.  In this way we can fool ourselves that we have made over 16 million colors.  And in that assumption belies our first and major problem.  We cannot guarantee that the color we print matches the color we chose on the VDU - and - we cannot guarantee that the color we see on the VDU matches the color we saw in the original scene.

You can check the color synthesis of any part of your image by moving the mouse or tablet pen over the image, and the RGB values are shown in the bottom of the screen.  The values show the color value under your pen or mouse.


colour rgb


In the Watercolour Tutorial, I wanted to emphasize the red in the figure to the left hand edge.  Red is a color which always wants to come to the fore.  Using the WACOM tablet and pen on the masking layer, I was able to enhance the red and make it really advance towards me.

Blue, which we always associate with sky, is recessive.  We use this distinction to give us information about depth and distance.  Green is seen as the colour of vegetation and tranquility.  It comes as no surprise that the middle of the spectrum visible to us, is green, and is the color to which our eyes have the greatest sensitivity.


colour whitianga


The Color Wheel


The color wheel is one way in which we try to make sense of color associations.  colors opposite to one another on this wheel have particular dynamism if close together in an image. 
If you look in Paint Shop Pro at
Adjust > Hue and Saturation > Hue/Saturation/Lightness you can see the color wheel representation being used.


colour hsl


So, blue and yellow are opposites, cyan (turquoise) and red, green and magenta (purple).  Fashionistas will tell you never to wear clothes that are color opposites because of this color dynamism.  But then, the dynamism can be used to pull attention in your photographs.

Any pair of colors directly opposite each other in the color wheel show this dynamism.  If we place the colors against each other, as in the square below, we can see their visual inmpact on each other.


colour square


Notice that intersecting lines from opposite sides of the wheel seem to “jar”.

I've marked the intersection which are opposite pairs.

When dyers, printers and serious photographers try to reproduce color, they use spectrophotometers to measure reflectance, and balanced light sources to compare samples in grey painted environments to prevent any influence from the surroundings.  As you attempt to print color, the next set of problems arise.

color dyes in inkjet printers and conventional photographic paper have limited archival lifetimes. Pigments although they are less light sensitive, are less easily applied.

Only if you are trying to perfectly color match the print with the original image do you need to consider the attribute of measure.  Most of the time, the attribute pleasure comes into play. 

Choose a well lit, strongly colored object and stare at it for at least 30 seconds.  Close your eyes and you will “see” the object but as a negative image; so a blue bath towel on the washing line will appear yellow in your mind when you’ve closed your eyes.

Yellow is the complementary color to blue.

Your brain reduced the value of the image in your brain, compensating for the color and the colours around it.  When you close your eyes the compensation remains, ie a yellow image.  For that reason you see the objects in a fluorescent lit room as normal; but really the room has an abundance of green light from the light source. 

It’s only when you look at the photos you took that you see the incorrect rendering unless, of course, you set the white balance correction in the camera!  But then you might set the White Balance to warm or cool the image, again this is all to do with mood.




Page Links

Light Waves

Color Wheel

Gamut

Colour In Your Software

The Colour Wheel








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